We use the term "vital unit" in the same restricted sense in which the materialists speak of "chemical units," "morphological units," etc., which they admit are invisible in the microscopic field, and hence they can have no positive information as to their destructibility or indestructibility by heat. That this vital unit lies, in its true functional tendencies, between the chemical and morphological units--manifesting itself in the conditions of the one and resulting in the structural development of the other--is no new or startling theory, but one that has been more or less obscurely hinted at by Leibnitz, and even acknowledged as possible by Herbert Spencer. It is this vital unit that assimilates or aggregates protoplasmic matter into the morphological cell, or the initial organism in a vital structure, or an approach towards structural form. Morphological cells are not therefore "units," considered as the least of any given whole, nor are they mere structureless matter, or any more homogeneous in character than in substance. Different chemical solutions give rise to different morphological cells, as differently constituted soils produce different vegetal growths. Change the chemical conditions in any solution or infusion, and you change the entire morphological character of the infusoria appearing therein.[28] The cells are living organisms springing from vital units, and can no more manifest themselves independently of these units than life can manifest itself independently of an actual organism. And they make their appearance in the proper environing conditions, just as the oak comes from its primordial germ or vital unit in the chemically changed conditions of the soil. Everywhere the vital germ or unit precedes the vital growth as the plant or tree precedes the natural seeds it bears.